Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle- or large-sized battery module having a plurality of battery cells electrically connected to each other because high power and large capacity are necessary for the middle or large-sized devices.
Preferably, the middle- or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle- or large-sized battery module. In particular, much interest is currently focused on such a pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight and the manufacturing cost of the pouch-shaped battery is low.
FIG. 1 is a perspective view typically showing a conventional representative pouch-shaped battery. A pouch-shaped battery 100 shown in FIG. 1 is configured to have a structure in which two electrode leads 110 and 120 protrude from the upper end and the lower end of a battery body 130, respectively, such that the electrode leads 110 and 120 are opposite to each other.
A sheathing member 140 includes upper and lower sheathing parts. That is, the sheathing member 140 is a two-unit member. In a state in which an electrode assembly (not shown) is mounted in a receiving part which is defined between the upper and lower sheathing parts of the sheathing member 140, opposite sides 140a and upper and lower ends 140b and 140c, which are contact regions of the upper and lower sheathing parts of the sheathing member 140, are bonded to each other, whereby the pouch-shaped battery 100 is manufactured. The sheathing member 140 is configured to have a laminate structure of a resin layer/a metal film layer/a resin layer. Consequently, it is possible to bond the opposite sides 140a and the upper and lower ends 140b and 140c of the upper and lower sheathing parts of the sheathing member 140, which are in contact with each other, to each other by applying heat and pressure to the opposite sides 140a and the upper and lower ends 140b and 140c of the upper and lower sheathing parts of the sheathing member 140 so as to weld the resin layers thereof to each other. According to circumstances, the opposite sides 140a and the upper and lower ends 140b and 140c of the upper and lower sheathing parts of the sheathing member 140 may be bonded to each other using a bonding agent.
For the opposite sides 140a of the sheathing member 140, the same resin layers of the upper and lower sheathing parts of the sheathing member 140 are in direct contact with each other, whereby uniform sealing at the opposite sides 140a of the sheathing member 140 is achieved by welding. For the upper and lower ends 140b and 140c of the sheathing member 140, on the other hand, the electrode leads 110 and 120 protrude from the upper and lower ends 140b and 140c of the sheathing member 140, respectively. For this reason, the upper and lower ends 140b and 140c of the upper and lower sheathing parts of the sheathing member 140 are thermally welded to each other, in a state in which a film type sealing member 160 is interposed between the electrode leads 110 and 120 and the sheathing member 140, in consideration of the thickness of the electrode leads 110 and 120 and the difference in material between the electrode leads 110 and 120 and the sheathing member 140, so as to improve sealability of the sheathing member 140.
However, the mechanical strength of the sheathing member 140 is low. For this reason, battery cells (unit cells) are mounted in a pack case, such as a cartridge, to manufacture a battery module having a stable structure. However, a device or a vehicle, in which a middle- or large-sized battery module is installed, has a limited installation space. Consequently, when the size of the battery module is increased due to the use of the pack case, such as the cartridge, the spatial utilization is lowered. Also, due to the low mechanical strength of the battery cells, the battery cells repeatedly expand and contract during charge and discharge of the battery cells. As a result, the thermally welded regions of the sheathing member may be easily separated from each other.
There have been proposed some technologies regarding module housings to cover outer surfaces of the pouch-shaped battery cells, thereby securing the safety of the battery cells.
For example, Japanese Patent Application Publication No. 2005-108693 discloses a technology regarding module housings including a pair of elastic parts, having the same elasticity, to support opposite major surfaces of a plate-shaped laminate battery cell.
The above technology proposes a structure to elastically press opposite major surfaces of the battery cell using the module housings, each of which is bent in a concave shape. However, the overall size of the battery cell is inevitably increased due to the additional attachment of the module housings to the opposite major surfaces of the battery cell. Also, it is required that the battery cell be inserted into the module housings with the above-stated construction. As a result, the assembly process is not easily performed, and therefore, mass production is difficult. That is, when the battery cell is forcibly inserted into the module housings, excessive load is applied to the battery cell with the result that the battery cell may be damaged.
Meanwhile, the thickness of battery cells (secondary batteries) may be changed during charge and discharge of the battery cells with the result that a gap may be formed between the battery cells. In this case, the battery cells may not be fixed in position when external impact or vibration is applied to the battery cells. Also, in a structure in which the battery cells are in direct contact with each other, the battery cells may easily slip from each other due to low frictional force between battery cases of the respective battery cells. As a result, the battery cell may move.
In a case in which the battery cells are not fixed in position but move due to various causes as described above, electrode terminal connection regions of the battery cells may be broken, or short circuits may occur in the battery cells. As a result, the safety and operational efficiency of the battery module are greatly lowered.
Consequently, there is a high necessity for a battery module that is compact, effectively buffers external impact, and exhibits excellent stability and safety.